Effect of surface charges on impulse flashover voltages of spacer in SF/sub 6/

The positive and negative charges were injected onto the spacer surface by DC corona discharges, and the flashover characteristics were investigated by a sudden change from DC to lightning or steep-fronted impulse in the presence of a conducting-particle attached on the spacer in SF/sub 6/ gas. Experimental results showed that the polarity of corona charges has a great influence on impulse flashover voltages. For the opposite polarity impulse to corona charges, there is a significant shift of the time domain where the minimum flashover voltage appears in the U-shaped curves of relationships between flashover voltage and wavefront duration (U/sub f/-t/sub f/). Also, the influence of DC polarity reversal on the corona discharge current has been studied.